To create heat necessary to burn insulation, one of two
problems must occur. Either too much current is being carried
on that wire (which is not likely) or a connection at the
point of burning is loose - causing a voltage drop at that
connection so high as to create heat. If the latter is true,
then what you though was a motor working just fine was
actually a motor under undue stress due to insufficient
voltage. IOW we have an example of a conclusion not based
upon the numbers.

Had you monitored that wall receptacle voltage when under
load, the problem would have been apparent then. The reason
we usually don't is that such failures are rare. But this is
the point. What you observed to be a fully functional system
was instead a system with one minor defect. Well such is life
and why being a human is so interesting.

If you don't find a loose screw at the point of burning
insulation, then we may have a much more serious problem. The
question that must be answered - why so much heat on that
wire? Maybe a trivial problem (ie loose screw) or maybe
symptoms of a human safety problem. Other posters have
provided useful background facts.

Seawulf wrote:
toller wrote:
I don't have an answer for you, just some questions...

1) Did you wire the subpanel correctly, with separated neutral
and ground buses?
2) The charring was away from the aluminum wire, right?

Yes, the neutrals are all connected to the neutral bus and the grounds
are connected to a separate ground bus on the opposite side of the box.

The 50A Al feed Neutral from the main box is connected by the large
screw to the top of the Neutral bus. It has no damage, nor do the other
Al wires.

The 220V circuit for the saws had been operating from the subpanel for
months before the two 120V circuits were added. The two 120V circuits
operated without any damage for at least a week or more after they were
installed. I know that because I had been removing the front panel
periodically assessing options for additional circuits for some time
after those 120V circuits were added.

I do not know when the damage occurred after that time. But, I do know
that the dust collector has operated and can still operate fine from
that damaged circuit Of course, at this point,I have secured power to
the entire subpanel until I can determine what caused the problem.

Thanks,
CW